Tiny plastic fragments buried in farmland for nearly two years did not become the chemical “sponges” scientists feared, according to a new study from researchers at the Hebrew University of Jerusalem. The findings suggest that aging polyethylene microplastics in agricultural soil has only a limited effect on their ability to capture and release organic contaminants such as pesticides, pharmaceuticals and wastewater-derived chemicals. Instead, the surrounding soil appears to remain the dominant force controlling where these substances travel and how long they persist.
Microplastics are increasingly common in agricultural landscapes, where they can enter soil through degraded greenhouse coverings, mulch films, irrigation water, sewage sludge and atmospheric deposition. Because these particles can remain in the environment for decades, researchers have questioned whether they might accumulate contaminants and transport them through soil, groundwater or food-production systems. The concern is particularly significant in regions where reclaimed wastewater is used to irrigate crops.
The study focused on linear low-density polyethylene, a flexible plastic widely used in agricultural films. Researchers buried fragments of previously used polyethylene mulch film in three different Israeli agricultural soils and allowed them to remain underground for 20 months. This approach was designed to reproduce environmental aging under realistic conditions rather than relying solely on accelerated laboratory treatments, which can produce surface changes that do not fully reflect what occurs in the field.
When the scientists recovered the plastic fragments, the particles had clearly changed. Natural organic matter from the soil had accumulated on their surfaces, forming a coating known as an environmental or soil-derived corona. Such coatings can alter surface chemistry, wettability and the availability of binding sites. In theory, these changes could increase the particles’ capacity to attract hydrophobic organic molecules, leading to stronger sorption and potentially allowing microplastics to act as mobile carriers of pollution.
To test that possibility, the researchers examined the interaction between the aged polyethylene and 48 organic contaminants commonly detected in reclaimed wastewater used for agricultural irrigation. The chemical set included pesticides, pharmaceuticals and other wastewater-associated compounds with different molecular properties. The team measured both sorption, the process by which contaminants attach to a surface, and desorption, the process by which they are released back into the surrounding environment.
The results challenged the assumption that aging automatically makes polyethylene microplastics more chemically active. For approximately 90 percent of the tested compounds, soil aging caused little or no meaningful change in the amount of contaminant associated with the plastic. Overall, the compounds interacted only weakly with the polyethylene and could be released relatively easily. That pattern indicates that the plastic did not permanently trap most of the chemicals or become a substantially more powerful contaminant carrier over time.
The researchers also found that the largest changes to the plastic surfaces occurred during the first year of burial. After that initial period, the particles became comparatively stable, suggesting that the formation of the organic coating reached a plateau. Surprisingly, differences among the three soils—including their organic matter and clay content—had little influence on how the polyethylene aged or how it interacted with the contaminants. This does not mean soil properties are unimportant; rather, it suggests that the soil matrix itself may dominate contaminant behavior more strongly than the aged plastic particles.
“Soil, not the plastic, remains the main factor influencing the environmental fate of these chemicals,” said Dr. Evyatar Ben Mordechay, one of the study’s researchers. Soil minerals, clay surfaces and native organic matter provide an enormous and chemically diverse network of binding sites. Compared with that complex matrix, the surface area and sorption capacity of polyethylene microplastics may be relatively minor, particularly when the particles are present at environmentally realistic concentrations.
The findings do not make microplastics harmless. Polyethylene fragments remain persistent pollutants, can accumulate in agricultural soils and may affect soil structure, organisms and ecosystem processes through other mechanisms. The study examined one plastic type, and different polymers, additives, particle sizes, shapes and weathering histories could behave differently. Even so, the research offers a more precise picture of their role in contaminant transport: for aged polyethylene in agricultural soils, the plastic appears to play a secondary part, while the soil itself continues to control the movement, retention and release of most organic pollutants.
Subject of Research: Cells
Article Title: Aging of polyethylene microplastics in agricultural soils has minimal effect on sorption and desorption of wastewater-derived organic contaminants
Web References: https://doi.org/10.1016/j.seh.2026.100207
References: Soil & Environmental Health, DOI: 10.1016/j.seh.2026.100207
Image Credits: Raz Lev
Keywords: Soil science, surface chemistry, environmental sciences, pollution, environmental chemistry, plastics, wastewater, microplastics, agricultural soils, organic contaminants
